Automatic transmissions or multiple-gear transmissions, which are generally known in the art, are predominantly based upon the principle of conventional manual transmissions in a gear building system, in which a gear shift is realized with control elements in the form of synchronizations. Because power-producing elements in these types of transmissions, designed in the form of spur gear levels, require a large installation space, in practice so-called automatic power shift gears with planetary gear sets are used. These require less installation space in comparison with transmissions comprising spur gear levels.
Automatic power shift gears, however, are designed with control elements, such as frictional multiple disk clutches and multiple disk breaks, that must have relatively large dimensions to enable transfer of torque, and are most often actuated hydraulically.
In addition, these types of power shift gears are disadvantageously characterized by large drag losses during their inoperative state or in their open state, and a correspondingly large amount of actuation energy is required for their actuation, which has a negative effect on the transmission efficiency.
Furthermore, transmission types are known in the art that are a combination of the two previously described transmission concepts, i.e., they combine automatic multiple-gear transmissions with a gear building system and automatic power shift transmissions with planetary gearsets.
Such a combination is represented, for example, by a conventional auxiliary transmission with power bifurcation and a post-connected planetary gearset as a summing transmission. The individual gears of such a transmission are engaged via the control elements of the auxiliary transmission, wherein the control elements as well as the spur gears of the spur gear levels of the power-bifurcated auxiliary transmission are located directly on a main shaft and directly on a countershaft.
The further the control elements and the spur gears, located on the two shafts of the auxiliary transmission, are distanced from a bearing of the main shaft and from a bearing of the countershaft in a transmission housing on the main shaft and on the countershaft, the higher are the tangential, radial, and axial forces that are exerted when the spur gear levels are hooked up. These forces lead to higher or lower bending moments or bending loads of the main shaft as well as the countershaft, so that both shafts must be dimensioned accordingly to avoid damage.
If very high drive moments are transferred via the transmission, the main shaft, the countershaft, and the bearings of the two shafts must be designed with undesirably large dimensions, resulting in the disadvantage of a high total weight of the transmission and high manufacturing costs for the transmission.
It is the task of the present invention to provide an automatic multiple-gear transmission with a reduced total weight and more economical manufacturing costs in comparison with automatic multiple-gear transmissions known in the art.